I was wondering if it is safe to put rocks found on a beach in a planted freshwater tank? I would obviously boil them first but is there any thing I might need to do in addition to that? I found some cool rocks and wanted to put them in my 10 gallon tank but don't want to harm the tank either. What are your opinions.

Rocks are rocks, regardless of where they come from. As long as it's a clean rock, of a type that's suitable for your water chemistry, you'll be fine. A lot of organisms you'd find on a beach rock will die off when exposed to fresh water anyway, but boiling and soaking will put you well on the safe side. Beaches are great places to look for rocks. Around here, you can find everything from quartz to granite to volcanic pumice to fossilized coral. Lots of good stuff out there, and it's all free for the taking.

Some rocks are not rocks, in that they're not OK. I put sandstone in my aquarium. Bad idea. When I removed through pieces, they were much smaller in size. Also my java fern roots decimated the one piece.

You see, sandstone looses cohesion and "melts" into sand when underwater.

In any case, as suggested the best test is to put some in a bucket and see what it does, both chemically and physically.

Thanks for the feedback. I don't have any pictures right now because I'm home for the weekend and the rocks are up in my dorm. I will take some pics when I get back though for sure. I was just looking for a few small rocks to add to my "river of rocks" in my 10 gallon tank. How do you tell the difference between all of those rocks you just spoke about? Like are there tell tale signs or something? I've always been curious about that lol

There are a few signs, but the bucket of water test that jsuereth mentioned is definitely the best. Usually stay away from brightly colored rocks, because thats a sign of high mineral content. Don't use any rocks you can break with your hands, or scratch with a fingernail or coin. And also, you can do a vinegar test by pouring a little bit of vinegar on the rock. Even if the rocks pass those tests I'd still let them spend a few days in a bucket of water with daily pH and hardness tests._________________Please, oh Please can someone help me!?

That's good advice. Unless you're sure, always play it safe. Granite is OK, as is quartz and slate. I believe marble might affect your pH, but I'd check on that to be sure. There are a number of field guides that deal with rocks and minerals - I think the Audubon guide is pretty cheap - maybe $14 (US) at Amazon. In this part of the world, (CT, USA) the vast majority of beach/river rocks are fine, but that isn't true everywhere.